Viewing devices for illuminating and enlarging microphotographic material provided on cassetted microfilm strips are known in the art, including U.S. Pat. Nos. 3,844,642 and 3,920,322. A motorized drive with both fast and slow forward and reverse movement of film for locating a particular frame of the cassetted film for illumination and viewing is also known in U.S. Pat. No. 3,920,322. The cassetted film may be enclosed in a projection chamber means which includes an intense light source and a projection lens as in the said patents, or the cassetted film may be located in an exposed condition as appears from U.S. Pat. No. 3,523,657. In prior constructions, with the presently known exception illustrated in FIG. 10 of U.S. Pat. No. 3,319,517, the optical axes of the light source, lens, all reflective mirror means and viewing screen of the viewing device are located in a single geometrical plane, which operates to limit the applicability of such viewing devices.
In the present invention, the path from the light source to the projection lens may be located in a plane that differs from the plane defined by light projection, or optical, axes after light leaves the projection lens, and this provides a desirable flexibility for usage of a micro image viewer. The light in the instant invention is projected from a source against a mirror, which mirror turns the light approximately 90.degree. to pass through a selected portion of the film in the cassette, and then through a projection lens to strike second and third direction-changing mirrors prior to impinging upon the illuminated viewing screen.
Previous viewers of cassetted microfilm suffered a common shortcoming that frequently the final viewing image of the selected microfilm portion lacked sufficient resolution to be clearly and easily distinguishable, particularly in an environment having a high intensity of ambient light.
The present invention, being a monitor primarily intended for use in motor vehicles, will be subject to bright ambient light. If the light were permitted to affect image resolution, the motor vehicle driver would be hampered in attempts to simultaneously read the monitor and exercise full and safe control over his vehicle.
It is accordingly one object of the present invention to provide a microfilm viewing monitor having an improved microfilm projection system, such that the clarity and resolution of the image are not affected by bright ambient light.
It is a further object of this invention to provide a microfilm viewing monitor of flexibility in use, specially adapted for mounting in motor vehicles so as to be readily viewable by the vehicle's driver.
These and other objects and advantages of the invention will become clear from the following description of a preferred embodiment of the invention.